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1 | Kernel driver adt7475 |
2 | ===================== |
3 | |
4 | Supported chips: |
5 | * Analog Devices ADT7473 |
6 | Prefix: 'adt7473' |
7 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
8 | Datasheet: Publicly available at the On Semiconductors website |
9 | * Analog Devices ADT7475 |
10 | Prefix: 'adt7475' |
11 | Addresses scanned: I2C 0x2E |
12 | Datasheet: Publicly available at the On Semiconductors website |
13 | * Analog Devices ADT7476 |
14 | Prefix: 'adt7476' |
15 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
16 | Datasheet: Publicly available at the On Semiconductors website |
17 | * Analog Devices ADT7490 |
18 | Prefix: 'adt7490' |
19 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
20 | Datasheet: Publicly available at the On Semiconductors website |
21 | |
22 | Authors: |
23 | Jordan Crouse |
24 | Hans de Goede |
25 | Darrick J. Wong (documentation) |
26 | Jean Delvare |
27 | |
28 | |
29 | Description |
30 | ----------- |
31 | |
32 | This driver implements support for the Analog Devices ADT7473, ADT7475, |
33 | ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in |
34 | minor details. The ADT7476 has additional features, including extra voltage |
35 | measurement inputs and VID support. The ADT7490 also has additional |
36 | features, including extra voltage measurement inputs and PECI support. All |
37 | the supported chips will be collectively designed by the name "ADT747x" in |
38 | the rest of this document. |
39 | |
40 | The ADT747x uses the 2-wire interface compatible with the SMBus 2.0 |
41 | specification. Using an analog to digital converter it measures three (3) |
42 | temperatures and two (2) or more voltages. It has four (4) 16-bit counters |
43 | for measuring fan speed. There are three (3) PWM outputs that can be used |
44 | to control fan speed. |
45 | |
46 | A sophisticated control system for the PWM outputs is designed into the |
47 | ADT747x that allows fan speed to be adjusted automatically based on any of the |
48 | three temperature sensors. Each PWM output is individually adjustable and |
49 | programmable. Once configured, the ADT747x will adjust the PWM outputs in |
50 | response to the measured temperatures without further host intervention. |
51 | This feature can also be disabled for manual control of the PWM's. |
52 | |
53 | Each of the measured inputs (voltage, temperature, fan speed) has |
54 | corresponding high/low limit values. The ADT747x will signal an ALARM if |
55 | any measured value exceeds either limit. |
56 | |
57 | The ADT747x samples all inputs continuously. The driver will not read |
58 | the registers more often than once every other second. Further, |
59 | configuration data is only read once per minute. |
60 | |
61 | Chip Differences Summary |
62 | ------------------------ |
63 | |
64 | ADT7473: |
65 | * 2 voltage inputs |
66 | * system acoustics optimizations (not implemented) |
67 | |
68 | ADT7475: |
69 | * 2 voltage inputs |
70 | |
71 | ADT7476: |
72 | * 5 voltage inputs |
73 | * VID support |
74 | |
75 | ADT7490: |
76 | * 6 voltage inputs |
77 | * 1 Imon input (not implemented) |
78 | * PECI support (not implemented) |
79 | * 2 GPIO pins (not implemented) |
80 | * system acoustics optimizations (not implemented) |
81 | |
82 | Special Features |
83 | ---------------- |
84 | |
85 | The ADT747x has a 10-bit ADC and can therefore measure temperatures |
86 | with a resolution of 0.25 degree Celsius. Temperature readings can be |
87 | configured either for two's complement format or "Offset 64" format, |
88 | wherein 64 is subtracted from the raw value to get the temperature value. |
89 | |
90 | The datasheet is very detailed and describes a procedure for determining |
91 | an optimal configuration for the automatic PWM control. |
92 | |
93 | Fan Speed Control |
94 | ----------------- |
95 | |
96 | The driver exposes two trip points per PWM channel. |
97 | |
98 | point1: Set the PWM speed at the lower temperature bound |
99 | point2: Set the PWM speed at the higher temperature bound |
100 | |
101 | The ADT747x will scale the PWM linearly between the lower and higher PWM |
102 | speed when the temperature is between the two temperature boundaries. |
103 | Temperature boundaries are associated to temperature channels rather than |
104 | PWM outputs, and a given PWM output can be controlled by several temperature |
105 | channels. As a result, the ADT747x may compute more than one PWM value |
106 | for a channel at a given time, in which case the maximum value (fastest |
107 | fan speed) is applied. PWM values range from 0 (off) to 255 (full speed). |
108 | |
109 | Fan speed may be set to maximum when the temperature sensor associated with |
110 | the PWM control exceeds temp#_max. |
111 | |
112 | Notes |
113 | ----- |
114 | |
115 | The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus. |
116 | Unfortunately, they fail to set the i2c adapter class, so this driver may |
117 | fail to find the chip until the nvidia driver is patched. |
118 |
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